The present invention relates generally to rotary cutters for cutting web material and the like, and more particularly to a novel self-adjusting rotary cutter apparatus which may be employed with a knife cylinder and associated anvil cylinder to effect single or double trim cuts transversely of a moving web or sheet and which facilitates reduced setup time, easier maintenance and longer knife blade life than has heretofore been attainable.
It is a conventional practice in the printing industry, and particularly in conjunction with web printing presses, to employ a rotary cutter assembly operative to transversely cut the web material received from the printing press. Such rotary cutters generally employ an anvil cylinder and a knife cylinder which are rotatable in timed relation about axes generally transverse to the direction of movement of the paper web and define a nip therebetween through which the web passes from the printing station. The knife cylinder carries one or more cutter assemblies having knife blades operative to cut or sever the web during rotation of the knife cylinder. Such rotary cutters may also be used with sheet printers to cut sheet material to predetermined length prior to passing it to a sheet type printing press.
When employed with web type printing presses, each cutter or knife assembly may carry a single knife blade to effect a single transverse cut through the moving web material, or may carry a pair of spaced knife blades operative to cut the web along parallel lines so as to create a trim or waste strip between the knife blades which is conventionally removed by means carried by the anvil or knife cylinder.
Known rotary cutter apparatus, and particularly variable rotary cutters for use in the web printing industry, exhibit a number of drawbacks which result in significant economic inefficiencies. For example, one known rotary cutter arrangement supports a pair of knife blades in an elastomeric holder having longitudinal slots which receive the knife blades. The elastomer holder is affixed to the outer periphery of a knife cylinder such that the holder yields during a cutting operation to take up radial inward movement of the cutting knives during engagement with the associated anvil cylinder. See, for example, U.S. Pat. No. 4,640,156. A drawback to such a rotary cutter arrangement is that the elastomeric material tends to take a permanent set after continued use and requires substantial maintenance to replace the blade holder or otherwise make adjustments so as to maintain the desired knife blade to anvil surface relation for efficient cutting. A further significant drawback in this type of rotary cutter arrangement is the inability to accurately adjust and maintain a desired cutting force between the cutting edges of the knife blades and the peripheral surface of the anvil cylinder.
Another known rotary web cutter apparatus supports one or more cutter blades generally longitudinally of a knife cylinder and allows for manual radial adjustment of the blades relative to the knife cylinder during rotation or roll-in of the knife cylinder so as to obtain the desired engagement of the knife blades against the anvil surface. See, for example, U.S. Pat. No. 4,466,319. Such rotary cutter apparatus require substantial setup time to precisely locate the knife blades relative to the anvil surface, and require significant downtime in the event of damage or wear to the knife blades.
As aforementioned, when employing pairs of spaced knife blades to effect parallel cuts transversely of a moving web and thereby create a waste or trim strip between the knife blades, it is desirable to provide means to remove the trim strip. One technique for removing trim strips utilizes a pin wheel operative to introduce generally radial pins between the pairs of knife blades and cause the trim strips to be released during rotation of the knife cylinder. A drawback in the use of such pin wheels lies in the low reliability of the pin wheel to completely remove a trim strip, thus leaving it between the corresponding knife blades where it is carried into the nip during the next successive web cutting cycle.
Thus, the know rotary web cutter apparatus exhibit a number of drawbacks which lead to operational and economic deficiencies due to the initital setup time required, the frequency of maintenance necessary to maintain proper operation and the relatively high skill level required for setup, maintenance and operation.